Devices for detecting and transmitting electrical pulses, e.g., EEG (electroencephalogram), ECG (electrocardiogram) and EIT (electric impedance tomography) cables, are used, for example, for electrocardiological measurements on patients in order to obtain information on the performance of the heart. Contacts are placed for this on the skin surface. The sum of these individual potentials can be measured on the body surface, and these are measured signals with very low frequencies, e.g., ranging from 0.1 Hz to 140 Hz, in the nV and μA ranges. In addition, by supplying an a.c. current with a frequency of, e.g., 40 kHz, the respiration parameters can be determined according to the so-called impedance method by means of the device.
Prior-art EEG, ECG and EIT cables have multiple shielding against external interferences, especially electromagnetic interferences and currents (artifacts), which distort weak measured signals. However, such EEG, ECG and EIT cables are expensive to manufacture, so that these cannot be employed for disposable use in patients for economic reasons.
U.S. Pat. No. 4,353,372 discloses a device for detecting and transmitting electrical pulses. A plurality of electrical leads of different lengths with an electrical insulating material are fixed at a first end to a connecting port for connection to the means processing the electrical pulses. The second ends of the leads of different lengths are provided with contacts to be placed on the skin surface of a patient. Due to the different lengths of the leads, different electrical resistances are present between the electrodes and the connecting port. The electrical resistance of the leads is directly proportional to the length of the electrical leads, i.e., the ratio of the electrical resistance to the length of the leads is constant. External interferences, especially electromagnetic interferences, in the leads disadvantageously induce different electric voltages and currents (artifacts) in the leads because of the different electrical resistances, and these electric voltages and currents can be filtered out by the means processing the electrical pulses only partially at best, for example, by means of stored algorithms. Thus, reliable and certain medical evaluation of the measured signals is not guaranteed.